The goal of flexible occlusion rendering (FOR) is to enable view-dependent rendering of occluded objects in a volume for displaying useful views of MRI and CT data to aid physicians in diagnosis. For example, when using volume rendering to perform virtual arthroscopy from a shoulder MRI, a view of the entire shoulder socket is desired for rapid evaluation of the cartilage surface for defects (FIG. 1). For example, FIG. 1 illustrates a textbook illustration of a shoulder socket. Such a view would be desirable in a real shoulder, but would require rendering from a viewpoint inside the humeral head. However, views from inside the humeral head that would otherwise show the entire socket are not possible, as the cartilage surface of the humeral head occludes the socket (FIG. 3, Camera 1). In FIG. 3, camera 1, indicated by reference number 10, represents a viewpoint inside of the humeral head. Such a view is difficult to achieve using standard rendering techniques because adjusting the volume rendering transfer function to reduce the opacity of the cartilage surface of the humeral head will also reduce the opacity of the cartilage surface of the shoulder socket, making the resulting image very difficult to interpret (FIG. 2). For example, FIG. 2 illustrates an image of a shoulder rendered from MRI data where the cartilage surfaces on the humeral head and in the shoulder socket are rendered with partial transparency. Because the cartilage surface of the shoulder socket is rendered with the same transparency as the cartilage surface of the humeral head, it is difficult to distinguish between the two surfaces in the resulting image, and defects are difficult to evaluate.
Therefore, with standard volume rendering, views of the shoulder socket are limited to those from positions within the fluid-filled joint capsule (FIG. 3, Camera 2, indicated by reference number 12) (reference number 10 and 12 will respectively be used to distinguish between Cameras 1 and 2 in the remaining figures that use such cameras to show different viewpoints). Because of this limitation, the physician must evaluate the socket from viewpoints either at extreme angles or very close to the surface, much like evaluating the surface of the hand with the palm touching the tip of the nose (Clarke, 2004). A method for removing the occluding material of the humeral head, enabling unobstructed views of the shoulder socket, is required. More generally, there exists a need for methods, systems, and computer readable media for flexible occlusion rendering, where images of surfaces can be rendered from arbitrarily selected viewpoints, regardless of the number and type of intervening interfaces between the viewpoint and the surface to be rendered.